Electric working machine and method for braking three-phase brushless motor of electric working machine

ABSTRACT

In one aspect of the present disclosure, an electric working machine includes a three-phase brushless motor, a first switching element, a second switching element, a third switching element, a fourth switching element, a fifth switching element, a sixth switching element, a rotation detector, a brake controller. The brake controller executes a two-phase short-circuit brake. The two-phase short-circuit brake is executed so as to switch any of the fourth switching element, the fifth switching element, and the sixth switching element to a corresponding ON-state or an OFF-state in response a detection signal from the rotation detector that occurs prior to a switching time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2017-117685 filed on Jun. 15, 2017 with the Japan Patent Office, theentire disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to an electric working machine thatincludes a three-phase brushless motor.

An electric working machine including a three-phase brushless motor as adriving source is configured to reduce or stop rotation of thethree-phase brushless motor by using a so-called short-circuit brake.The short-circuit brake is achieved through three terminals of thethree-phase brushless motor to be shorted, which generates a brakingforce on the three-phase brushless motor.

The short-circuit brake in general use is a three-phase short-circuitcontrol, where a brake current flows into all phases of the three-phasebrushless motor. Such a three-phase short-circuit control generates anexcessive braking force, which results in increase in force that isapplied to an electric apparatus due to the braking force and thus afailure may occur in the electric apparatus.

In respective electric working machines disclosed in Japanese UnexaminedPatent Application Publication No. 2013-243824 and Japanese UnexaminedPatent Application Publication No. 2017-070102, a two-phaseshort-circuit control is executed to thereby generate a desired brakingforce. In the two-phase short-circuit control, only two current pathsare completed among three current paths between respective threeterminals of a three-phase brushless motor and a positive electrode of adirect-current power source. Alternatively, only two current paths arecompleted among three current paths between the respective threeterminals and a negative electrode of the direct-current power source.

In the two-phase short-circuit control, as shown in FIG. 7, for example,three high-side switches are tuned off. The high-side switches areswitching elements that are provided on the three current paths betweenthe respective three terminals corresponding to a U-phase, a V-phase,and a W-phase of the three-phase brushless motor and the positiveelectrode (H-side) of the direct-current power source.

On the other hand, three low-side switches are tuned on and off inaccordance with rotation of the three-phase brushless motor. Thelow-side switches are switching elements that are provided on the threecurrent paths between the respective terminals of the three-phasebrushless motor and the negative electrode (L-side) of thedirect-current power source.

To execute the two-phase short-circuit control, used is a rotationsensor that provides detection signals (Hall signals shown in FIG. 7)every time the motor rotates by a specific angle (every 60-degree inelectrical angle, in FIG. 7).

In the two-phase short-circuit control, a delay time is set in a timerevery time the motor rotates by the specific angle (at every timeperiods indicated by arrows in FIG. 7) that corresponds to the detectionsignals from the rotation sensor, and then measurement by the timer isstarted (a time point t1). The delay time corresponds to a time (a timecorresponding to 30 degrees in electrical angle, in FIG. 7) until any ofthe low-side switches is next switched to an ON-state or an OFF-state.

In response to elapse of the delay time and an end of the measurement bythe timer (a time point t2), any of the low-side switches is switched tothe ON-state or the OFF-state in accordance with a specific switchingpattern.

SUMMARY

In general, a rotation sensor includes three Hall elements. Therespective three Hall elements correspond to a U-phase, a V-phase, and aW-phase of a three-phase brushless motor and are arranged at respectiveintervals of 120 degrees in electrical angle, in general.

If the Hall elements are deviated in position, a variation occurs inchange time periods in respective detection signals (Hall signals) fromthe rotation sensor. As a result, the detection signals do not changeevery time the motor rotates by a specific angle (for example, 60degrees in electrical angle).

Such a variation in the intervals (the change time periods) between therespective detection signals leads to a variation in respective delaytimes that are set in a timer, and this may consequently result in afailure to execute a brake control properly.

Specifically, as exemplary illustrated in FIG. 8, if the change timeperiods (t) in the respective Hall signals for the U-phase, the V-phase,and the W-phase are uneven as a result of the Hall elements beingdeviated in position, the intervals T1, T2, and T3 . . . between therespective detection signals become uneven. Consequently, this leads tounevenness of the delay times D1, D2, and D3 . . . , respectively, thatare set based on the intervals T1, T2, and T3 . . . .

In such a circumstance, as shown in the upper section of FIG. 8, if thedelay times D1, D2, and D3 . . . , respectively, are 50% of therespective intervals between the detection signals T1, T2, and T3 . . .(in a case where percentage is set as 50% in the timer), errors betweenthe respective delay times D1, D2, and D3 . . . as a result of thevariation in the respective Hall signals for the U-phase, the V-phase,and the W-phase is small. Thus, this is not developed into a significantproblem.

For example, the delay times D1, D2, and D3 . . . , respectively, areset to 80% of the respective intervals between the detection signals T1,T2, and T3 . . . (in a case where the percentage is set as 80% in thetimer) so as to reduce a braking force that is generated by the brakecontrol. In this case, however, the errors between the respective delaytimes D1, D2, and D3 . . . are greater in comparison with the case wherethe percentage is set as 50% in the timer.

Consequently, as shown in “before countermeasure” in the middle sectionof FIG. 8, if, as a result of the errors, the long delay time D1 is setin the timer, this may cause the next delay time D2 to be set in thetimer before elapse of the delay time D1.

In this case, as shown in a dotted line in FIG. 8, the brake control(switching of any of the low-side switches to the corresponding ON-stateor the OFF-state) that should be executed in response to the elapse ofthe delay time D1 set in the timer at the corresponding change timeperiod in the corresponding detection signal may not be executed.

In one aspect of the present disclosure, it is desirable to inhibit afailure to properly execute a two-phase short-circuit brake on athree-phase brushless motor of an electric working machine as a resultof a variation in an interval in a detection signal from a rotationsensor.

In one aspect of the present disclosure, an electric working machineincludes a three-phase brushless motor, a first switching element, asecond switching element, a third switching element, a fourth switchingelement, a fifth switching element, a sixth switching element, arotation detector, and a brake controller. The three-phase brushlessmotor includes a first terminal, a second terminal, and a thirdterminal. The first switching element is provided between the firstterminal and a first electrode of a direct-current power source. Thefirst switching element is configured to electrically couple the firstterminal to the first electrode in an ON-state. The first switchingelement is configured to electrically decouple the first terminal fromthe first electrode in an OFF-state. The second switching element isprovided between the second terminal and the first electrode. The secondswitching element is configured to electrically couple the secondterminal to the first electrode in an ON-state. The second switchingelement is configured to electrically decouple the second terminal fromthe first electrode in an OFF-state. The third switching element isprovided between the third terminal and the first electrode. The thirdswitching element is configured to electrically couple the thirdterminal to the first electrode in an ON-state. The third switchingelement is configured to electrically decouple the third terminal fromthe first electrode in an OFF-state. The fourth switching element isprovided between the first terminal and a second electrode of thedirect-current power source. The fourth switching element is configuredto electrically couple the first terminal to the second electrode in anON-state. The fourth switching element is configured to electricallydecouple the first terminal from the second electrode in an OFF-state.The fifth switching element is provided between the second terminal andthe second electrode. The fifth switching element is configured toelectrically couple the second terminal to the second electrode in anON-state. The fifth switching element is configured to electricallydecouple the second terminal from the second electrode in an OFF-state.The sixth switching element is provided between the third terminal andthe second electrode. The sixth switching element is configured toelectrically couple the third terminal to the second electrode in anON-state. The sixth switching element is configured to electricallydecouple the third terminal from the second electrode in an OFF-state.

The rotation detector generates a detection signal that indicates arotation position of the three-phase brushless motor every time thethree-phase brushless motor rotates by a specific angle. The rotationdetector may include, for example, the above-described Hall elements.

The brake controller executes a two-phase short-circuit brake. Thetwo-phase short-circuit brake is executed so as to set the firstswitching element, the second switching element, and the third switchingelement to the respective OFF-states and to switch any of the fourthswitching element, the fifth switching element, and the sixth switchingelement to the corresponding ON-state or the OFF-state in accordancewith a switching time that is based on the detection signal. Thetwo-phase short-circuit brake is further executed so as to switch any ofthe fourth switching element, the fifth switching element, and the sixthswitching element to the corresponding ON-state or the OFF-state inresponse to the detection signal that occurs prior to the switchingtime.

With the electric working machine configured as mentioned above, the anyof the fourth switching element, the fifth switching element, and thesixth switching element is ensured to be switched to the correspondingON-state or the OFF-state in response to the detection signal thatoccurs prior to the switching time.

Thus, the electric working machine can inhibit the failure to properlyexecute the two-phase short-circuit brake as a result of the variationin an interval in the detection signal.

The above-described electric working machine may include a timer that isconfigured to measure a time. In this case, the brake controller mayinclude a timer setter that is configure to set in the timer a delaytime until arrival of the switching time based on the detection signaland to start measurement for the delay time by the timer.

The brake controller may further include a switching controller that isconfigured to switch the any of the fourth switching element, the fifthswitching element, and the sixth switching element to the correspondingON-state or the OFF-state in response to completion of the measurementfor the delay time by the timer.

The timer setter may be configured to switch, in place of the switchingcontroller, the any of the fourth switching element, the fifth switchingelement, and the sixth switching element to the corresponding ON-stateor the OFF-state in response to the delay time being newly set in thetimer based on the detection signal before elapse of the delay time thatis previously set in the timer.

In this case, the variation occurs in the interval in the detectionsignal and the delay time that is previously set may not be elapsed whenthe timer setter newly sets the delay time in the timer. Even in thiscase, it is possible to execute the two-phase short-circuit brake thatcorresponds to the previously set delay time.

Thus, it is possible to inhibit the failure to properly execute thetwo-phase short-circuit brake due to the variation in the interval inthe detection signal.

In a case where the timer setter switches, in place of the switchingcontroller, the any of the fourth switching element, the fifth switchingelement, and the sixth switching element to the corresponding ON-stateor the OFF-state, this may be performed at a time period as it shouldbe.

The timer setter may be configured to switch, in response to the delaytime being newly set in the timer based on the detection signal beforeelapse of the delay time that is previously set in the timer, the any ofthe fourth switching element, the fifth switching element, and the sixthswitching element to the corresponding ON-state or the OFF-state withina specific time after the rotation position of the three-phase brushlessmotor reaches a specific rotation position that is acquired based on thedetection signal.

Alternatively, the timer setter may be configured to switch, in responseto the delay time being newly set in the timer based on the detectionsignal before elapse of the delay time that is previously set in thetimer, the any of the fourth switching element, the fifth switchingelement, and the sixth switching element to the corresponding ON-stateor the OFF-state immediately after the rotation position of thethree-phase brushless motor reaches a specific rotation position that isacquired based on the detection signal.

The first electrode may correspond to a positive electrode of thedirect-current power source and the second electrode may correspond to anegative electrode of the direct-current power source.

Alternatively, the first electrode may correspond to a negativeelectrode and the second electrode may correspond to a positiveelectrode.

The brake controller may be configured to execute the two-phase shortcircuit brake in response to establishment of a brake condition duringthe three-phase brushless motor rotating.

Another aspect of the present disclosure is a method for braking athree-phase brushless motor of an electric working machine. The methodmay include generating a detection signal that indicates a rotationposition of the three-phase brushless motor every time the three-phasebrushless motor rotates by a specific angle.

The method may include setting a first switching element, a secondswitching element, and a third switching element to respectiveOFF-states in response to establishment of a brake condition during thethree-phase brushless motor rotating, the first switching element beingprovided between a first terminal of the three-phase brushless motor anda first electrode of a direct-current power source, the first switchingelement being configured to electrically couple the first terminal tothe first electrode in an ON-state, the first switching element beingconfigured to electrically decouple the first terminal from the firstelectrode in the OFF-state, the second switching element being providedbetween a second terminal of the three-phase brushless motor and thefirst electrode, the second switching element being configured toelectrically couple the second terminal to the first electrode in anON-state, the second switching element being configured to electricallydecouple the second terminal from the first electrode in the OFF-state,the third switching element being provided between a third terminal ofthe three-phase brushless motor and the first electrode, the thirdswitching element being configured to electrically couple the thirdterminal to the first electrode in an ON-state, and the third switchingelement being configured to electrically decouple the third terminalfrom the first electrode in the OFF-state.

The method may include switching any of a fourth switching element, afifth switching element, and a sixth switching element to acorresponding ON-state or an OFF-state in accordance with a switchingtime that is based on the detection signal in response to theestablishment of the brake condition during the three-phase brushlessmotor rotating, the fourth switching element being provided between thefirst terminal and a second electrode of the direct-current powersource, the fourth switching element being configured to electricallycouple the first terminal to the second electrode in the ON-state, thefourth switching element being configured to electrically decouple thefirst terminal from the second electrode in the OFF-state, the fifthswitching element being provided between the second terminal and thesecond electrode, the fifth switching element being configured toelectrically couple the second terminal to the second electrode in theON-state, the fifth switching element being configured to electricallydecouple the second terminal from the second electrode in the OFF-state,the sixth switching element being provided between the third terminaland the second electrode, the sixth switching element being configuredto electrically couple the third terminal to the second electrode in theON-state, and the sixth switching element being configured toelectrically decouple the third terminal from the second electrode inthe OFF-state.

The method may include switching the any of the fourth switchingelement, the fifth switching element, and the sixth switching element tothe corresponding ON-state or the OFF-state in response to the detectionsignal that occurs prior to the switching time.

With such a method, it is possible to inhibit a failure to properlyexecute the two-phase short-circuit brake for the three-phase brushlessmotor as a result of a variation in an interval in the detection signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, an example embodiment of the present disclosure will bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a grinder showing a configuration of thegrinder in a present embodiment;

FIG. 2 is a block diagram showing a configuration of a motor drivecircuit that is provided to the grinder;

FIG. 3 is a flowchart showing control process that is executed in acontrol circuit;

FIG. 4 is a flowchart showing a detail of a motor control process;

FIG. 5 is a flowchart showing a signal interruption process that isexecuted in the control circuit;

FIG. 6 is a flowchart showing a timer interruption process that isexecuted in the control circuit;

FIG. 7 is a time chart showing respective changes in Hall signals, drivesignals, and phase currents in a two-phase short-circuit control; and

FIG. 8 is a time chart illustrating a defect in the two-phaseshort-circuit control that results from a variation in an input intervalin a detection signal and a countermeasure therefor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present embodiment, a grinder that performs, for example,grinding, polishing, and cutting of a material to be processed will bedescribed as one example of an electric working machine of the presentdisclosure.

As shown in FIG. 1, a grinder 2 of the present embodiment includes amotor housing 4, a gear housing 6, and a rear housing 8. The motorhousing 4, the gear housing 6, and the rear housing 8 may be integrallyassembled to each other to form a main body portion of the grinder 2.

The motor housing 4 may be formed in a cylindrical shape. The motorhousing 4 may have the outer diameter that allows a user of the grinder2 to grip the motor housing 4 with one hand. The motor housing 4 housesa motor 5 shown in FIG. 2 in the motor housing 4. The motor 5 of thepresent embodiment is a three-phase brushless motor.

The motor 5 is arranged in the motor housing 4 such that a rotationshaft of the motor 5 is in parallel with and substantially coaxial withthe central axis of the motor housing 4. The rotation shaft of the motor5 protrudes toward the gear housing 6.

As with the motor housing 4, the rear housing 8 may be formed in asubstantially cylindrical shape. The rear housing 8 is located in afirst longitudinal end of the motor housing 4 (specifically, at a sideopposite to the gear housing 6). In a first longitudinal end of the rearhousing 8 (specifically, at a side opposite to the motor housing 4), anattachment portion 9 is located. The attachment portion 9 has a firstbattery pack 20A and a second battery pack 20B that are detachablyattached to the attachment portion 9.

The attachment portion 9 houses therein a motor drive circuit 30 shownin FIG. 2.

The rear housing 8 includes a trigger switch 16. The trigger switch 16is configured such that the user can perform a pulling operation of thetrigger switch 16 while gripping the rear housing 8.

The gear housing 6 is located in a second longitudinal end of the motorhousing 4 (specifically, at a side opposite to the rear housing 8). Thegear housing 6 houses a gear mechanism. The gear mechanism is configuredto transmit a rotation of the motor 5 to an output shaft that isperpendicular to the rotation shaft of the motor 5. The output shaftprotrudes from the gear housing 6. To the protruded portion of theoutput shaft, fixed is a tip tool 10 having a circular-plate shape, suchas a grinding wheel and a cutting-off wheel.

Accordingly, the grinder 2 is designed to rotate the tip tool 10 inresponse to driving of the motor 5, to thereby enable grinding,polishing, and cutting works.

Further, there may be disposed a wheel cover 12 around the tip tool 10.The wheel cover 12 eliminates or reduces dust that is generated duringthe grinding, polishing, and cutting works from dispersing toward theuser, to thereby protect the user.

The wheel cover 12 may be formed in a substantially semicircular shapeso as to cover a portion of (substantially a half of) the tip tool 10from a gear housing 6-side. The wheel cover 12 may be fixed via aring-shaped fixing member 14 around a portion of the gear housing 6 fromwhich the output shaft protrudes.

As shown in FIG. 2, the motor drive circuit 30 is supplied with electricpower from the first battery pack 20A and the second battery pack 20Bthat are connected in series. The motor drive circuit 30 is configuredto perform a drive control of the motor 5 such that the motor 5 isdriven and stopped corresponding to an operation state of the triggerswitch 16. Specifically, the motor drive circuit 30 includes a bridgecircuit 32, a gate circuit 34, a control circuit 36, and a regulator 40.

The bridge circuit 32 is configured to supply from the first batterypack 20A and the second battery pack 20B an electric current to a notshown U-phase winding, a not shown V-phase winding, and a not shownW-phase winding of the motor 5, respectively. The bridge circuit 32 ofthe present embodiment includes six switching elements Q1 to Q6 andforms a so-called three-phase full bridge circuit.

The switching elements Q1 to Q3 are provided as so-called high-sideswitches, respectively, between terminals U, V, and W of the motor 5 anda positive electrode power-supply line. The terminals U, V, and W,respectively, are coupled to the U-phase winding, the V-phase winding,and the W-phase winding. The positive electrode power-supply line iscoupled to a positive electrode of the first battery pack 20A.Respective positive electrode-side current paths between the terminalsU, V, and W of the motor 5 and the positive electrode power-supply lineare completed when the respective switching elements Q1 to Q3 are placedin respective ON-states.

The switching elements Q4 to Q6 are provided as so-called low-sideswitches, respectively, between the terminals U, V, and W and a groundline. The ground line is coupled to a negative electrode of the secondbattery pack 20B. Respective negative electrode-side current pathsbetween the terminals U, V, and W of the motor 5 and the ground line arecompleted when the respective switching elements Q4 to Q6 are placed inrespective ON-states.

Further, in the present embodiment, each of the switching elements Q1 toQ6 may be an n-channel metal oxide silicon field-effect transistor(MOSFET). In this case, respective diodes (so-called, parasitic diodes)are connected in parallel to the switching elements Q1 to Q6 betweenrespective drains and sources of the switching elements Q1 to Q6. Aforward direction of each diode corresponds to a source-to-draindirection.

Accordingly, in respective OFF-states of the switching elements Q1 toQ6, each diode allows the electric current to flow in a reversedirection from the negative electrode side of the second battery pack20B to the positive electrode side of the first battery pack 20A.

The gate circuit 34 is configured to turn on and off the switchingelements Q1 to Q6 in accordance with respective control signalsoutputted from the control circuit 36. With such an operation of thegate circuit 34, a drive current or a motor brake current is supplied tothe U-phase winding, the V-phase winding, and the W-phase winding of themotor 5, thus rotating and braking the motor 5.

The control circuit 36 is configured to control driving and braking ofthe motor 5 via the gate circuit 34. The control circuit 36 includes aMicro Control Unit (MCU) that includes a CPU, a ROM, and a RAM. Thecontrol circuit 36 includes a non-volatile memory 38 for storingrespective states (for example, failure state) of the motor 5 and themotor drive circuit 30 that are controlled by the control circuit 36.The control circuit 36 may include, instead of or in addition to theMCU, a combination of individual electronic components, ApplicationSpecified Integrated Circuit (ASIC), Application Specific StandardProduct (ASSP), a programmable logic device such as Field ProgrammableGate Array (FPGA), or the combination thereof.

The control circuit 36 is coupled to the above-described trigger switch(SW) 16 and a LED-display 18 that is located on the motor housing 4 orthe rear housing 8.

In addition, the control circuit 36 is coupled to a battery voltagedetector 24, an electric current detection circuit 26, and a rotationdetector 28. The control circuit 36 controls the motor 5 based onrespective detection signals that are outputted from the trigger SW16,the battery voltage detector 24, the electric current detection circuit26, and the rotation detector 28.

The battery voltage detector 24 detects a value of a voltage(hereinafter referred to as a “battery voltage value”) that is suppliedfrom the first battery pack 20A and the second battery pack 20B.

The electric current detection circuit 26 is located between the bridgecircuit 32 and the ground line and detects a value of an electriccurrent (hereinafter referred to as a “motor current value”) that flowsthrough the motor 5.

The rotation detector 28 generates the detection signals every time themotor 5 rotates by a specific angle (60 degrees in electrical angle, inthe present embodiment). The rotation detector 28 includes three Hallelements that are arranged at respective intervals of 120 degrees inelectrical angle. The respective three Hall elements correspond to theU-phase winding, the V-phase winding, and the W-phase winding.

As shown in FIG. 7, the rotation detector 28 configured as mentionedabove outputs respective three Hall signals that correspond to theU-phase winding, the V-phase winding, and the W-phase winding.Differences in phase between the respective Hall signals are 120 degreesin electrical angle. Based on changes in the Hall signals, the controlcircuit 36 is able to detect a rotation speed of the motor 5.

In other words, in response to detection of an edge of each Hall signalwhere a logical value of each Hall signal is inverted, the controlcircuit 36 determines that the above-described detection signal isinputted. The control circuit 36 detects the rotation speed of the motor5 based on a time interval in inputting the detection signals and arotation angle (60 degrees in electrical angle).

Further, the control circuit 36 recognizes a rotational position of themotor 5 based on the detection signals from the rotation detector 28, tothereby control a time for switching the switching elements Q1 to Q6 tothe respective ON-states or OFF-states. Such an operation of the controlcircuit 36 controls the electric current that flows through the motor 5during the driving and the braking of the motor 5.

Hereinafter, a description is given to a control process that isexecuted in the control circuit 36 to control the driving and thebraking of the motor 5.

As shown in FIG. 3, the control circuit 36 repeatedly executes a seriesof processes S120 to S150 (S refers to a step) in a specific controlcycle (a time-base).

Specifically, the control circuit 36 determines in S110 whether thetime-base is elapsed to thereby wait for the specific control cycle tobe elapsed (S110: NO). In response to determination in S110 that thetime-base is elapsed (S110: YES), the control circuit 36 proceeds to aprocess in S120.

In S120, the control circuit 36 executes a switch operation detectionprocess. In this process, the control circuit 36 confirms an ON-stateand an OFF-state of the trigger SW16 to thereby detect operation of thetrigger SW16 made by the user. In response to completion in executingthe switch operation detection process, the control circuit 36 proceedsto a process in S130.

In S130, the control circuit 36 executes an analog-digital (A/D)conversion process. In this process, the control circuit 36 converts thedetection signal outputted from the battery voltage detector 24 and thedetection signal outputted from the electric current detection circuit26 from an analog form to a digital form (A/D conversion) and acquiresconverted detection signals.

In the subsequent S140, the control circuit 36 executes a motor controlprocess. In this process, the control circuit 36 controls the drivingand the braking of the motor 5 based on the ON state and the OFF stateof the trigger SW16, the battery voltage value, and the motor currentvalue that are read by the control circuit 36 in S120 and S130.

In the subsequent S150, the control circuit 36 executes a displayprocess. In this process, the control circuit 36 detects a state of adriving system of the motor 5 and a state of a braking system of themotor 5 based on the battery voltage value and the motor current value,and displays the detected states via the LED-display 18. In the displayprocess, the control circuit 36 controls, for example, a lighting coloror a lighting pattern of the LED-display 18 to thereby identifiablydisplay to the user: whether the grinder 2 is under proper operation;and a detail of a failure state upon occurrence a failure. The controlcircuit 36 returns to the process in S110 in response to completion ofthe display process.

The motor control process in S140 will be described in detail. As shownin FIG. 4, the control circuit 36 determines in S210 whether the triggerSW16 is placed in the ON-state. If the trigger SW16 is not placed in theON-state (S210: NO), a drive command for the motor 5 is not inputted tothe control circuit 36. Accordingly, the control circuit 36 proceeds toa process in S240.

In response to determination in S210 that the trigger SW16 is placed inthe ON-state (S210: YES), the control circuit 36 proceeds to a processin S220 and determines, based on the above-described battery voltagevalue and the motor current value, whether the motor 5 can be driven.

If the motor 5 can be driven (S220: YES), the control circuit 36proceeds to a process in S230 to drive the motor 5. If the motor 5cannot be driven (S220: NO), the control circuit 36 proceeds to aprocess in S240.

In S230, the control circuit 36 executes a motor driving process. Inthis process, the control circuit 36 calculates a drive duty ratio forthe bridge circuit 32 so as to gradually increase the rotation speed (orthe drive current) of the motor 5 to a target rotation speed (or atarget current value) to thereby control the motor 5 to be placed in atarget rotation state. The control circuit 36 terminates the motordriving process in response to completion of the motor control process.

In S240, the control circuit 36 determines, based on the above-describedchanges in the Hall signals, whether the motor 5 is currently inrotation and requires a braking force to be generated (in other words,determines whether a condition for executing a brake control isestablished).

If execution of the brake control is required (S240: YES), the controlcircuit 36 proceeds to a process in S250, sets a brake flag, and thenterminates the motor control process. Conversely, if the execution ofthe brake control is not required (S240: NO), the control circuit 36proceeds to a process in S260, clears the brake flag, and thenterminates the motor control process.

A description will be given to a signal interruption process that isexecuted by the control circuit 36 every time the motor 5 rotates by 60degrees in electrical angle in accordance with the detection signals(specifically, the respective Hall signals corresponding to the U-phasewinding, the V-phase winding, and the W-phase winding) from the rotationdetector 28.

As shown in FIG. 5, in the signal interruption process, the controlcircuit 36 determines in S310 whether the brake flag is set. If thebrake flag is set (S310: YES), the control circuit 36 proceeds to aprocess in S320 and determines whether a soft brake process requirementis set. The soft brake process requirement is provided to requestexecution of a two-phase short-circuit brake, which is set in a processsubsequent to S320.

If the soft brake process requirement is not set (S320: NO), the controlcircuit 36 proceeds to a process in S340 and acquires an elapsed timesince the preceding signal interruption process is started. In responseto completion in acquiring the elapsed time, the control circuit 36proceeds to a process in S350.

In S350, the control circuit 36 calculates a delay time based on theelapsed time that is acquired in S340 and a delay angle that is set inadvance. The delay time corresponds to a period of time from a start ofthe signal interruption process until the switching elements Q1 to Q6are next switched to the respective ON-states or the OFF-states.

The delay angle is an angle such as “30 degrees in electrical angle” asexemplary illustrated in FIG. 7. Specifically, the delay angle is set atthe above-described ratio such as 50% and 80% with respect to therotation angle (60 degrees in electrical angle) that corresponds to theelapsed time. Accordingly, the control circuit 36 calculates the delaytime in S350 by multiplying a specific ratio (50% or 80%) with theelapsed time acquired in S340 that corresponds to a specific rotationangle.

In response to completion in calculating the delay time, the controlcircuit 36 sets the calculated delay time in a timer in the subsequentprocess in S360 and starts measurement of the delay time. Finally, thecontrol circuit 36 sets in S370 the soft brake process requirement andterminates the signal interruption process.

In response to determination in S310 that the brake flag is not set(S310: NO), the control circuit 36 proceeds to a process in S380,executes a process other than the braking such as the motor driving, andthen terminates the signal interruption process.

At a time period where the delay time set in the timer is elapsed, thecontrol circuit 36 starts a timer interruption process shown in FIG. 6.

In the timer interruption process, the control circuit 36 firstdetermines in S410 whether the soft brake process requirement is set. Ifthe soft brake process requirement is set (S410: YES), the controlcircuit 36 proceeds to a brake control process in S420. In this process,the control circuit 36 allows the motor 5 to generate the braking forcewith the two-phase short-circuit brake.

In the brake control process, the control circuit 36 maintains, asexemplary illustrated in FIG. 7, all of the high-side switches (Q1 toQ3) to be in the respective OFF-states, and sequentially switches eachof the low-side switches (Q4 to Q6) to the corresponding ON-state or theOFF-state in a specific pattern.

Accordingly, the control circuit 36 identifies in S420 the low-sideswitch that should be switched from the corresponding ON-state tocorresponding the OFF-state, or from the corresponding OFF-state to thecorresponding ON-state in the currently executed timer interruptionprocess based on a specific control pattern, and then switches theidentified low-side switch to the corresponding ON-state or theOFF-state (see, a time point t2) to thereby achieve the two-phaseshort-circuit brake.

Subsequent to execution of the brake control process mentioned above,the control circuit 36 proceeds to a process in S430, clears the softbrake process requirement, and then terminates the timer interruptionprocess.

In response to determination in S410 that the soft brake processrequirement is not set (S410: NO), the control circuit 36 proceeds to aprocess in S440, executes a process other than the braking such themotor driving, and then terminates the timer interruption process.

The process in S440 is executed on the basis that the delay time set inthe timer in S380 in the signal interruption process is elapsed, whichinterlocks with the process in S380.

In the motor driving, for example, it is necessary to appropriately turnon the switching elements Q1 to Q6 at the drive duty ratio that isobtained in the above-described motor driving process in S230.

Accordingly, in S380 in the signal interruption process, the controlcircuit 36 sets, via the timer, respective times at which the switchingelements Q1 to Q6 are switched to the respective ON-states or theOFF-states in a specific drive pattern. Further, in S440 of the timerinterruption process, the control circuit 36 identifies, in accordancewith the specific drive pattern, the switching element that should beswitched to the corresponding ON-state or the OFF-state in the currentlyexecuted timer interruption process, and then switches the identifiedswitching element to the corresponding ON-state or the OFF-state.

As described above, the control circuit 36 executes, in the timerinterruption process, the brake control process in S420 to therebyachieves the two-phase short-circuit brake. However, when a variationoccurs in interval between the detection signals (the Hall signals) fromthe rotation detector 28, as indicated in the middle section of FIG. 8,the delay time is set in the timer in the signal interruption processbefore switching the low-side switches to the respective ON-states orOFF-states in the timer interruption process. As a result, the brakecontrol may not be executed properly.

In the present embodiment, if it is determined, in S320 in the signalinterruption process shown in FIG. 5, that the soft brake processrequirement is set, the signal interruption process proceeds to theprocess in S330 since the brake control process is not executed by thetimer interruption process. Then, the brake process that should beexecuted in the timer interruption process is executed in S330 in placeof the timer interruption process.

Consequently, as indicated in the lower section of FIG. 8, when thesignal interruption process is executed without execution of the brakecontrol process in the timer interruption process, the control circuit36 enables in the signal interruption process the execution of the brakecontrol (switching of the switching elements to the respective ON-statesor the OFF-states) that should be executed in the timer interruptionprocess.

Thus, the grinder 2 in the present embodiment enables the brake controlto be properly executed even where the variation occurs in intervalbetween the detection signals (the Hall signals) inputted from therotation detector 28 and the next detection signal is inputted during atime period until elapse of the delay time set in the timer in thesignal interruption process.

In the present embodiment, the control circuit 36 corresponds to oneexample of the brake controller of the present disclosure. In addition,of the control process that is executed by the control circuit 36, thesignal interruption process achieves a function as one example of thetimer setter of the present disclosure; and the timer interruptionprocess achieves a function as one example of the switching controllerof the present disclosure.

Although one embodiment of the present disclosure has been describedabove, the present disclosure is not limited to the aforementionedembodiment and may be modified in various forms.

For example, in the aforementioned embodiment, the soft brake processrequirement is set in S320 in the signal interruption process. If it isdetermined that the brake control process is not executed in the timerinterruption process, the control circuit 36 immediately executes thebrake control process in S330.

However, the brake control process should be, in fact, executed at atime period at which the remaining time that should be measured in thetimer is elapsed. Accordingly, the control circuit 36 may execute thebrake control process in S330 in response to elapse of the remainingtime.

It should be noted that measurement of the remaining time requiresproviding of another timer for measuring the remaining time in additionto the timer that is used to execute the timer interruption process.This may complicate the control process that is executed by the controlcircuit 36.

Accordingly, in response to determination in S320 in the signalinterruption process that the soft brake process requirement is set(S320: YES), the control circuit 36 may proceed to a delaying process inS325 and waits for a specific time until the brake control process inS330 is executed.

In the aforementioned embodiment, the two-phase short-circuit brake isexecuted so as to set the high-side switches (Q1 to Q3) to therespective OFF-states and to switch any of the low-side switches (Q4 toQ6) to the corresponding ON-state or the OFF-state in accordance withthe rotation of the motor 5.

However, the low-side switches (Q4 to Q6) may be set in the respectiveOFF-states and any of the high-side switches (Q1 to Q3) may be switchedto the corresponding ON-state or the OFF-state to thereby execute thetwo-phase short-circuit brake.

The brake control for the motor 5 may be executed by a combination ofthe above-described two-phase short-circuit brake and the all-phase (orthe three-phase) short-circuit brake.

In the aforementioned embodiment, a description has been given to thegrinder 2 that is configured to drive the motor 5 by electric powersupply from the first battery pack 20A and the second battery pack 20B.However, the electric working machine of the present disclosure is notlimited to such a grinder.

The electric working machine of the present disclosure may be, forexample, any kind of electric working machine that includes a batterypack. In addition, the electric working machine of the presentdisclosure may be operated by the electric power supply from an externaldirect-current power source such as an alternating current (AC) adapteror operated by the electric power supply from an AC power source such asa power source for commercial use.

In addition, two or more functions of one element in the aforementionedembodiment may be achieved by two or more elements; or one function ofone element in the aforementioned embodiment may be achieved by two ormore elements. Likewise, two or more functions of two or more elementsmay be achieved by one element; or one function achieved by two or moreelements may be achieved by one element. A part of the configuration ofthe aforementioned embodiment may be omitted; and at least a part of theconfiguration of the aforementioned embodiment may be added to orreplaced with another part of the configuration of the aforementionedembodiment. It should be noted that any and all modes that areencompassed in the technical ideas that are defined only by thelanguages in the claims are embodiments of the present disclosure.

What is claimed is:
 1. An electric working machine, comprising: a tool;a three-phase brushless motor including a first terminal, a secondterminal, and a third terminal and configured to generate a drivingforce for driving the tool; a first high-side switch provided betweenthe first terminal and a positive electrode of a direct-current powersource, the first high-side switch being configured to electricallycouple the first terminal to the positive electrode in an ON-state, andthe first high-side switch being configured to electrically decouple thefirst terminal from the positive electrode in an OFF-state; a secondhigh-side switch provided between the second terminal and the positiveelectrode, the second high-side switch being configured to electricallycoupled the second terminal to the positive electrode in an ON-state,and the second high-side switch being configured to electricallydecouple the second terminal from the positive electrode in anOFF-state; a third high-side switch provided between the third terminaland the positive electrode, the third high-side switch being configuredto electrically couple the third terminal to the positive electrode in aON-state, and the third high-side switch being configured toelectrically decouple the third terminal from the positive electrode inan OFF-state; a first low-side switch provided between the firstterminal and a negative electrode of the direct-current power source,the first low-side switch being configured to electrically couple thefirst terminal to the negative electrode in an ON-state, and the firstlow-side switch being configured to electrically decouple the firstterminal from the negative electrode in an OFF-state; a second low-sideswitch provided between the second terminal and the negative electrode,the second low-side switch being configured to electrically couple thesecond terminal to the negative electrode in an ON-state, and the secondlow-side switch being configured to electrically decouple the secondterminal from the negative electrode in an OFF-state; a third low-sideswitch provided between the third terminal and the negative electrode,the third low-side switch being configured to electrically couple thethird terminal to the negative electrode in an ON-state, and the thirdlow-side switch being configured to electrically decouple the thirdterminal from the negative electrode in an OFF-state; a rotationdetector configured to generate a detection signal that indicates arotation position of the three-phase brushless motor every time thethree-phase brushless motor rotates by a specific angle; and a controlcircuit configured to execute a signal interruption process and a timerinterruption process, wherein the control circuit is configured toexecute the signal interruption process in response to occurrence of thedetection signal, wherein the signal interruption process includes:executing a brake control process in response to a soft brake processrequirement being set, the soft brake process requirement requestingexecution of a two-phase short-circuit brake; calculating a delay timebased on an elapsed time since the signal interruption process ispreviously executed and a delay angle; and setting the delay timecalculated in a timer to start measurement of the delay time by thetimer, wherein the control circuit is further configured to execute thetimer interruption process in response to elapse of the delay time,wherein the timer interruption process includes: executing the brakecontrol process in response to the soft brake process requirement beingset; and clearing the soft brake process requirement in response tocompletion of the brake control process, and wherein the brake controlprocess includes: setting the first high-side switch, the secondhigh-side switch, and the third high-side switch to the respectiveOFF-states; and switching any one of the first low-side switch, thesecond low-side switch, and the third low-side switch to thecorresponding ON-state or the OFF-state in accordance with the rotationposition of the three-phase brushless motor so as to place any two ofthe first low-side switch, the second low-side switch, and the thirdlow-side switch to the respective ON-states and to place any remaininglow-side switch of the first low-side switch, the second low-sideswitch, and the third low-side switch in the corresponding OFF-state. 2.An electric working machine, comprising: a three-phase brushless motorincluding a first terminal, a second terminal, and a third terminal; afirst switching element provided between the first terminal and a firstelectrode of a direct-current power source, the first switching elementbeing configured to electrically couple the first terminal to the firstelectrode in an ON-state, and the first switching element beingconfigured to electrically decouple the first terminal from the firstelectrode in an OFF-state; a second switching element provided betweenthe second terminal and the first electrode, the second switchingelement being configured to electrically couple the second terminal tothe first electrode in an ON-state, and the second switching elementbeing configured to electrically decouple the second terminal from thefirst electrode in an OFF-state; a third switching element providedbetween the third terminal and the first electrode, the third switchingelement being configured to electrically couple the third terminal tothe first electrode in an ON-state, and the third switching elementbeing configured to electrically decouple the third terminal from thefirst electrode in an OFF-state; a fourth switching element providedbetween the first terminal and a second electrode of the direct-currentpower source, the fourth switching element being configured toelectrically couple the first terminal to the second electrode in anON-state, and the fourth switching element being configured toelectrically decouple the first terminal from the second electrode in anOFF-state; a fifth switching element provided between the secondterminal and the second electrode, the fifth switching element beingconfigured to electrically couple the second terminal to the secondelectrode in an ON-state, and the fifth switching element beingconfigured to electrically decouple the second terminal from the secondelectrode in an OFF-state; a sixth switching element provided betweenthe third terminal and the second electrode, the sixth switching elementbeing configured to electrically couple the third terminal to the secondelectrode in an ON-state, and the sixth switching element beingconfigured to electrically decouple the third terminal from the secondelectrode in an OFF-state; a rotation detector configured to generate adetection signal that indicates a rotation position of the three-phasebrushless motor every time the three-phase brushless motor rotates by aspecific angle; and a brake controller configured to execute a two-phaseshort-circuit brake, wherein the two-phase short-circuit brake isexecuted so as to set the first switching element, the second switchingelement, and the third switching element to the respective OFF-statesand to switch any of the fourth switching element, the fifth switchingelement, and the sixth switching element to the corresponding ON-stateor the OFF-state in accordance with a switching time that is based onthe detection signal, and wherein the two-phase short-circuit brake isfurther executed so as to switch any of the fourth switching element,the fifth switching element, and the sixth switching element to thecorresponding ON-state or the OFF-state in response to the detectionsignal that occurs prior to the switching time.
 3. The electric workingmachine according to claim 2, further comprising a timer that isconfigured to measure a time, wherein the brake controller includes atimer setter that is configured to set in the timer a delay time untilarrival of the switching time based on the detection signal and to startmeasurement for the delay time by the timer.
 4. The electric workingmachine according to claim 3, wherein the brake controller includes aswitching controller that is configured to switch the any of the fourthswitching element, the fifth switching element, and the sixth switchingelement to the corresponding ON-state or the OFF-state in response tocompletion of the measurement for the delay time by the timer.
 5. Theelectric working machine according to claim 4, wherein the timer setteris configured to switch, in place of the switching controller, the anyof the fourth switching element, the fifth switching element, and thesixth switching element to the corresponding ON-state or the OFF-statein response to the delay time being newly set in the timer based on thedetection signal before elapse of the delay time that is previously setin the timer.
 6. The electric working machine according to claim 3,wherein the timer setter is configured to switch, in response to thedelay time being newly set in the timer based on the detection signalbefore elapse of the delay time that is previously set in the timer, theany of the fourth switching element, the fifth switching element, andthe sixth switching element to the corresponding ON-state or theOFF-state within a specific time after the rotation position of thethree-phase brushless motor reaches a specific rotation position that isacquired based on the detection signal.
 7. The electric working machineaccording to claim 3, wherein the timer setter is configured to switch,in response to the delay time being newly set in the timer based on thedetection signal before elapse of the delay time that is previously setin the timer, the any of the fourth switching element, the fifthswitching element, and the sixth switching element to the correspondingON-state or the OFF-state immediately after the rotation position of thethree-phase brushless motor reaches a specific rotation position that isacquired based on the detection signal.
 8. The electric working machineaccording to claim 2, wherein the first electrode corresponds to apositive electrode of the direct-current power source, and wherein thesecond electrode corresponds to a negative electrode of thedirect-current power source.
 9. The electric working machine accordingto claim 2, wherein the first electrode corresponds to a negativeelectrode of the direct-current power source, and wherein the secondelectrode corresponds to a positive electrode of the direct-currentpower source.
 10. The electric working machine according to claim 2,wherein the brake controller is configured to execute the two-phaseshort-circuit brake in response to establishment of a brake conditionduring the three-phase brushless motor rotating.
 11. A method forbraking a three-phase brushless motor of an electric working machine,the method comprising: generating a detection signal that indicates arotation position of the three-phase brushless motor every time thethree-phase brushless motor rotates by a specific angle; setting a firstswitching element, a second switching element, and a third switchingelement to respective OFF-states in response to establishment of a brakecondition during the three-phase brushless motor rotating, the firstswitching element being provided between a first terminal of thethree-phase brushless motor and a first electrode of a direct-currentpower source, the first switching element being configured toelectrically couple the first terminal to the first electrode in anON-state, the first switching element being configured to electricallydecouple the first terminal from the first electrode in the OFF-state,the second switching element being provided between a second terminal ofthe three-phase brushless motor and the first electrode, the secondswitching element being configured to electrically couple the secondterminal to the first electrode in an ON-state, the second switchingelement being configured to electrically decouple the second terminalfrom the first electrode in the OFF-state, the third switching elementbeing provided between a third terminal of the three-phase brushlessmotor and the first electrode, the third switching element beingconfigured to electrically couple the third terminal to the firstelectrode in an ON-state, and the third switching element beingconfigured to electrically decouple the third terminal from the firstelectrode in the OFF-state; switching any of a fourth switching element,a fifth switching element, and a sixth switching element to acorresponding ON-state or an OFF-state in accordance with a switchingtime that is based on the detection signal in response to theestablishment of the brake condition during the three-phase brushlessmotor rotating, the fourth switching element being provided between thefirst terminal and a second electrode of the direct-current powersource, the fourth switching element being configured to electricallycouple the first terminal to the second electrode in the ON-state, thefourth switching element being configured to electrically decouple thefirst terminal from the second electrode in the OFF-state, the fifthswitching element being provided between the second terminal and thesecond electrode, the fifth switching element being configured toelectrically couple the second terminal to the second electrode in theON-state, the fifth switching element being configured to electricallydecouple the second terminal from the second electrode in the OFF-state,the sixth switching element being provided between the third terminaland the second electrode, the sixth switching element being configuredto electrically couple the third terminal to the second electrode in theON-state, and the sixth switching element being configured toelectrically decouple the third terminal from the second electrode inthe OFF-state; and switching the any of the fourth switching element,the fifth switching element, and the sixth switching element to thecorresponding ON-state or the OFF-state in response to the detectionsignal that occurs prior to the switching time.